The application of coating materials using electrostatic spraying techniques has been practiced in industry for many years. In these applications, the coating material is discharged in atomized form, and an electrostatic charge is imparted to the atomized particles which are then directed toward a substrate maintained at a different potential to establish an electrostatic attraction for the charged, atomized particles. In the past, coating materials of the solvent-based variety, such as varnishes, lacquers, enamels and the like, were the primary materials employed in electrostatic coating applications. The problem with such coating materials is that they create an atmosphere which is both explosive and toxic. The explosive nature of the environment presents a safety hazard should a spark inadvertently be generated, such as by accidentally grounding the nozzle of the spray gun which can ignite the solvent in the atmosphere causing an explosion. The toxic nature of the workplace atmosphere created by solvent coating materials can be a health hazard should an employee inhale solvent vapors.
As a result of the concerns with solvent-based coatings, the recent trend has been to switch to water-based coating materials which reduce the problems of explosiveness and toxicity. Nevertheless, this switch to water-based type coatings has sharply increased the risk of electrical shock, which risk was relatively minor with solvent-based coatings. The problem of electrical shock has been addressed in U.S. Pat. Nos. 5,078,168; 5,197,676; and, a number of related patents owned by the assignee of this invention. In systems of the type disclosed in these patents, a "voltage block," i.e., an air gap, is provided between one or more sources of the conductive coating material and the electrostatically charged coating material which is directed to the coating dispensers. This voltage block ensures that there is never an electrical path between the source of water-based or other electrically conductive coating material, and the high voltage electrostatic power supply.
A variety of water-based, electrically conductive coating materials are commercially available which are suitable for use in voltage block systems of the type described above. In some applications, however, it is desirable to employ coating materials formed of the combination of two components, i.e., a catalyst and a resin. These two-component coating materials are produced by combining a metered quantity of the catalyst with a metered quantity of resin within a mixing device, and then discharging the intermixed components to one or more dispensers for application onto a substrate.
The same problems of explosiveness and toxicity mentioned above in connection with coating materials generally, apply to two-component coating materials formed by the combination of a resin and catalyst. This problem has been addressed by the development of water-based, two-component coating materials which reduce or eliminate problems of explosiveness and toxicity, but create the same problems of potential electrostatic shock as other water-based coatings when employed in electrostatic spraying systems. There has therefore been a need for an electrostatic spraying system capable of the formation of a water-based or electrically conductive, two-component coating material, which also reduces electrical shock hazard when employing electrostatic spraying techniques.